Method for Operating a Processing Machine

ABSTRACT

A method for operating a processing machine, in which a first web section of a product web is delimited by closing a first clamping point and a second clamping point, such that a first web tensile force prevails in the web section. A third clamping point within the first web section is closed, so that a second web section is formed between the first clamping point and the third clamping point. At least one of the closed third clamping point and the closed first clamping point are adjusted by an angle, so that a second web tensile force in the second web section is changed, preferably increased.

This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2012 006 792.5, filed on Apr. 4, 2012 in Germany, and to patent application no. DE 10 2012 013 435.5, filed on May 7, 2012 in Germany, the disclosures of which are incorporated herein by reference in their entirety.

BACKGROUND

The present disclosure relates to a method for operating a processing machine.

Although the disclosure will be described below essentially with reference to printing machines, it is not restricted to such an application but instead can be used in all types of processing machines in which a tensile force of a product web or material web is to be predefined. The product web can be formed from paper, material, paperboard, plastic, metal, rubber, in the form of film or foil, and so on.

Web processing machines, such as printing machines, in particular in gravure printing machines, screen printing machines and inline flexographic printing machines, have printing units, for example, as processing devices and one or more other processing devices, such as dryers, an embosser or punch. If the product web is clamped in during processing, such as in most printing units or embossers, these are generally to be designated clamping processing devices or clamping points. The material web is subdivided by clamping points into various web sections also possibly having different web tensile force values, since a clamping point in the “closed” state clamps the product web in and forms a frictionally fitting unit. After a certain time, the web tensile force is established in a steady state in the sections (with an assumed constant rotational speed of the cylinders and therefore conveying speed of the web).

In web processing machines it is widespread practice to control or regulate the web tensile force and the processing register in order to achieve an optimal processing result. In processing devices with rotating cylinders, such as printing units or embossers, as is known to the responsible person skilled in the art, this is done for example by means of what are known as angular adjustments or changes to the rotational speed. In the case of an angular adjustment, a rotating cylinder of the clamping point is rotated through a specific angle in addition to its usual rotational movement. If the product web is clamped in by this cylinder, as a result the product web is stretched on one side of the clamping point and compressed on the other side of the clamping point. As a result, this is normally also associated with a change in the web tension in the adjacent sections.

The structural plan of a machine 100 having printing units 111, 112, 113 and an additional processing device formed as an embosser 110 (this can be, for example, an embosser, a punch or the like) is shown schematically by the FIGURE by using a gravure printing machine: each printing unit comprises a printing cylinder 111 a, 112 a, 113 a and an impression cylinder, which are set against each other and clamp the product web 101 in. The printing cylinders in what are known as shaftless machines (i.e. without any common driveshaft=“king shaft”) are each driven by an individual motor (not shown). Likewise, the embosser 110 comprises a driven embossing cylinder 110 a and an impression cylinder. The printing machine 100 is controlled by a computing unit 200, which is set up by programming and communicates with actuators (e.g. motors) and sensors (e.g. register mark sensors, rotational angle sensors).

After each printing unit there are a dryer 102 and a cooling roll 103, respectively. Before the printing units there is a driven infeed unit 115 and, at the end of the processing, a driven outfeed unit 114. Infeed unit and outfeed unit are likewise clamping points, which clamp the product web in.

Here, between the last printing unit 111 and the outfeed unit 114, there is the embosser 110 as a further processing station 110. Often, the last cooling roll (after the last printing unit in the FIGURE) is displaced after the further processing station, so that this last processing is still carried out on the heated product web. It is of particular significance that the further processing station also clamps the web in, in exactly the same way as the printing units, and must also operate in a register-maintaining manner. For example, an embossing pattern must be oriented exactly on a printed image.

In addition, the diameter of the processing stations is normally staggered in such a way that the diameters in the web running direction are always chosen to be slightly larger in order to compensate for a lengthening or stretching of the product web established by the processing (e.g. input of moisture, heating) or the transport (tension), and therefore of the processing steps already carried out (e.g. individual color separations). This also makes it easier to maintain a desired web tensile force. The diameter of the embossing cylinder 110 a is normally chosen to be considerably larger than that of the printing cylinders 111 a-113 a, since the web normally stretches noticeably on the long path to the embosser as a result of the input of ink and the drying and heating.

Instead of a gravure printing machine with additional processing station connected downstream, the disclosure can also be applied to other printing processes, such as (narrow-web) flexographic printing, screen printing or any other type of processing operations. There, too, processing stations are normally connected downstream after the printing units.

It is desirable, when starting up such a processing machine, to obtain maintenance of register between all the processing devices quickly, in order to produce as little waste as possible. This presents difficulties in particular for a processing station which has to “re”-process a noticeably lengthened web, e.g. has to apply an embossing pattern to a printed image whilst maintaining register. As a result of the noticeably different cylinder diameters described, following the closure of the (previously registered, i.e. angularly correct) embosser, a gradual rise in the web tensile force in the section before the embosser occurs since, in general, in the transient state, the web tension is considerably lower after the closed embosser than before the closed embosser and since, when the embosser is closed, the web tension between the last printing unit and the outfeed unit has the lower actual web tension value of the intended web tension after the embosser. As a result, register errors occur during the transient process of the web tension, so that rejects are produced until the web tensile force has reached its final value.

In DE 10 2007 053 527 A1, presetting of the web tensile force at a standstill is described. Transferred to this application, the open embosser 110 would be set to a register-maintaining angular value (what is known as pre-registration) and, by means of the outfeed unit 114, a web tensile force would be set in the area between the last printing unit 111 and outfeed unit 114, and the embosser 110 would then be closed. This solution cannot be applied optimally to the case present here, since the resultant web tensile force in the section before the embosser depends highly on the drying behavior and therefore cannot be predicted accurately. Even when the web tensile force is preset at a standstill, a transient process after starting up can therefore hardly be avoided. Furthermore, many outfeed units are not capable of delivering the high web tensile force caused by the embosser.

In DE 10 2006 004 307 A1 and EP 1 981 791 B1, presetting the web tensile force for printing units is described. In this case, however, noticeable web lengthening does not normally occur. For the presetting, by means of additionally necessary measuring elements between the printing units, a web tensile force is established by means of angular adjustment. This solution cannot therefore be applied well to the case present here either since, as explained, the resultant web tensile force in the section before the embosser cannot be predicted. In addition, when the impression cylinder of the embosser is lifted following a determination of the resultant steady-state web tensile force, the web tensile force before the embosser will dip once more, since a lower web tensile force is run after the embosser.

Another way would be to regulate the web tensile force by means of appropriate activation of the processing devices and to regulate the processing register via the web tensile force set point. To this end, the embosser is closed following pre-registration and the web tensile force is subsequently regulated by means of a web tensile force controller. The register controller prescribes a necessary web tensile force set point, which means that the web tensile force controller establishes a web tensile force and a higher-order register controller controls the web tensile force controller. The starting value of the web tensile force set point is determined, for example, by using preceding production runs and is retrievable in a database. This results in cascade control, the dynamics of which are relatively low because of the two controllers. In addition, two cascaded controllers have to be adjusted, which is complicated. Furthermore, for example, fine gearing compensation of the embosser is set here by means of a web tensile force controller. In the steady state, however, the register controller must ensure that this fine gearing compensation becomes 0 since otherwise, on account of the electronic gearing (1:1) between the printing units and the register-maintaining embosser, a register error would build up in the event of fine gearing compensation not being equal to 0. This means that the register controller with its (reactive) dynamics must ensure that it stipulates a web tensile force set point such that a fine gearing compensation of 0 results. This can be achieved by it only on the basis of register errors which occur or do not occur, which in turn does not have an optimal influence on the duration of the transient.

It is desirable to accelerate a setup procedure of a processing machine in which a gradual web tension change is caused by closing a clamping point.

SUMMARY

According to the disclose, a method for operating a processing machine is described. Advantageous refinements of the method are also described herein.

A computing unit according to the disclosure, for example a control device of a printing machine, is set up, in particular by programming, to carry out a method according to the disclosure.

In addition, the implementation of the disclosure in the form of software is advantageous, since this permits particularly low costs, in particular if an executing computing unit is also used for further tasks and is therefore present in any case. Suitable data storage media for providing the computer program are in particular floppy disks, hard drives, flash memories, EEPROMs, CD-ROMs, DVDs and many more. A download of a program via computer networks (Internet, Intranet and so on) is also possible.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a block diagram view of a processing machine configured to be operated according to a method, as described herein.

DETAILED DESCRIPTION

The method disclosed herein creates a possible way of accelerating the starting up or setting up of a processing machine (in particular as far as a state with steady web tensile force and fault-free register) in which, as a result of the closing of a clamping point, a gradual web tension change is caused, and of reducing waste as a result. By way of the method, setting up and transient processes of the web tensile force and register controller are shortened, so that time and rejects are saved (costs of material and printing ink).

Within the context of the disclosure, a method is proposed for operating a processing machine, in which a web section is delimited by a first and a second clamping point and a web tension prevails in the web section, in which a third clamping point within this web section (i.e. between the first and the second clamping point) is closed, wherein the web tension in one of the web sections delimited by the third clamping point is then increased to a specific value quickly and specifically by means of appropriate action of an adjusting means. Therefore, the gradual process is shortened and register control can operate substantially normally substantially immediately after the increase. Rejects are reduced as a result. The method includes regulated, controlled or combined setting of a web tensile force which, as far as possible, corresponds to the final web tensile force, and simultaneous/subsequent engagement of the register control. Additionally or alternatively, the web stretch can be adjusted appropriately.

It is recommended also to act on the adjusting means of downstream web sections in such a way that the change in the web tensile force is balanced out. If, for example, clamping points arranged downstream of the third clamping point are also adjusted (“cascaded”), the web tensile force in web sections after the third clamping point barely changes. At the third clamping point (e.g. embosser) and following axes (such as outfeed unit, winder), actuating commands of the printing units can also be pre-controlled, as described, for example, in DE 10 2005 019 566 A1, DE 10 2007 017 095 A1 or DE 10 2009 005 820 A1.

The third clamping point itself can be used as an adjusting means, for example by an angular position and/or a rotational speed of a rotating cylinder of the clamping point being adjusted.

If the third clamping point itself is used as adjusting means and an angular position of a rotating cylinder of the clamping point is adjusted, the adjustment angle is preferably calculated from the diameters of the third clamping point and the other clamping point delimiting the relevant web section. In the sense of the disclosure, a rotating cylinder, which clamps the product web in, of the third clamping point, for example a printing cylinder, embossing cylinder, transfer cylinder and so on, is adjusted by a specific angle following the closure. This is intended to achieve the situation in which the resultant web tensile force, otherwise established in the steady state only gradually, is built up substantially immediately. The angle to be adjusted is determined from the diameters of the cylinders delimiting the web section (for example of an embossing cylinder and a printing cylinder preceding the embosser) and from the web length between the cylinders which delimit the web section. Dryer lengths, estimated or determined moduli of elasticity, a dryer temperature and/or a moisture content of the material can preferably be taken into account.

Assuming a homogeneous material in the web section (e.g. between the last printing unit and embosser), the result in the steady state is a locally independent stretch ε_(DW−PR)(x,t)=ε_(DW−PR) in this area.

Given knowledge of the diameters of embosser D_(PR) and printing unit D_(DW) and the length of the web between the printing unit and the embosser L_(DW−PR), the additional stretch of this web section in direct comparison with the stretch at the printing unit ε_(DW) is

${\Delta \; ɛ_{{DW},{PR}}} = {\frac{D_{PR} - D_{DW}}{D_{DW}}.}$

The angle to be adjusted is then

$\frac{D_{PR} - D_{DW}}{D_{DW}} \cdot {L_{{DW} - {PR}}.}$

If the material is not homogenous, such as can be the case, for example, when a dryer is used, the result is a non-constant modulus of elasticity E(x,t) in this area. Given knowledge of the variation in the modulus of elasticity or by means of estimating the same, the web length L_(DW−PR) can be corrected by an amount or factor. If, for example, the material is considerably “softer” (lower E) in the dryer than directly before the embosser at which the register is determined by means of a register sensor, then a considerably greater web length will have to be assumed.

$\frac{D_{PR} - D_{DW}}{D_{DW}} \cdot {L_{{DW} - {PR}^{corr}}.}$

It is recommended to align the third clamping point with the product web before the closure, i.e. to carry out pre-registration, so that the clamping point is in register following the closure and the processing is carried out in the correct position on the product web.

The action of an adjusting means, in order as a result to increase the web tensile force in the one of the web sections delimited by the third clamping point rapidly and specifically to a specific value, can also be carried out within the context of web tensile force control. By means of the web tensile force control (in a computing unit), the web tensile force in the relevant web section is adjusted, for example via fine gearing compensation (i.e. a change in the rotational speed), via an additive speed value or via an angular adjustment. The intended web tensile force can, for example, be measured in preceding production runs and subsequently stored. When the desired actual web tensile force is reached, the web tensile force control is switched off and any fine gearing compensation or additive speed that is present is removed. If an angular adjustment has been carried out, this is maintained. The register control can be activated at any desired time following the closure of the clamping point; advantageous for example is the time at which controller output variables of the tensile force control (e.g. fine gearing compensation) are removed.

According to a further embodiment, firstly, following the closure of the third clamping point, an angular adjustment is carried out in order to obtain very fast presetting of the web tensile force, and the intended web tensile force is subsequently set (e.g. to a previously measured value) by means of the web tensile force control.

According to a preferred embodiment of the disclosure, at least one controller parameter for regulating a register at the second clamping point arranged after the third clamping point and/or for regulating a web tensile force in the web section between the third and the second clamping point, for example an outfeed unit, has different values for whether the third clamping point is closed or not. As a result of opening and closing the third clamping point, the effective web length of the web section between the first and second clamping point changes (i.e. first to second or first to third and third to second). Controller parameters, such as a proportional gain K_(P) or a reset time T_(N), can be predefined as a function of the length of the web section. Thus, the controller parameters are preferably matched to the shortest and/or longest web length, since here the smallest and largest values have to be set. When the third clamping point is opened, for example, the web tensile force control, which acts on the second clamping point, can be provided with controller parameters which are adapted to the whole of the web length between the first and second clamping point.

It goes without saying that the features mentioned above and still to be explained below can be used not only in the respectively specified combination but also in other combinations or on their own without departing from the context of the present disclosure.

With reference to the FIGURE, a preferred embodiment of the disclosure will now be explained. According to the embodiment of the disclosure described here, the web tensile force in the web section between the printing unit 111 as first clamping point and the embosser 110 as third clamping point is to be brought as quickly as possible to the steady-state value following the closure of the embosser, without firstly having to wait for a gradual transient process. This is because, during the transient, the processing register (longitudinal register, circumferential register) cannot be controlled practically, so that rejects are produced. When the embosser is open, the web section is delimited by the outfeed unit 114 as second clamping point.

When the machine 100 is set up, first of all the printing units 111-113 are brought to a register-maintaining state, so that a good printed image is produced. The embosser 110 is then pre-registered. To this end, the embossing cylinder 110 a is aligned such that, after the latter has been thrown on or during the closure, the embossing pattern is located exactly on the printed image on the product web. As described, because of the lengthening of the product web, the diameter D_(PR) of the embossing cylinder 110 a is noticeably greater than the diameter D_(DW) of the printing cylinder 111 a but these two rotate equally fast, so that following the closure of the embosser 110, a noticeable rise in the web tensile force in the web section between printing unit 111 and embosser 110 is expected. In order to shorten this gradual rise, the embossing cylinder 110 a is rotated by a specific angle φ in addition to a usual rotation substantially immediately following the closure of the embosser 110, in order to cause an increase in the web tensile force. The angle φ is calculated from the aforesaid diameters and the length L_(DW−PR) between the printing unit 111 and the embosser 110 in accordance with:

$\phi = {\frac{D_{PR} - D_{DW}}{D_{DW}} \cdot {L_{{DW} - {PR}}.}}$

Because of the clamping embosser, as a result of the angular adjustment, the web is also displaced by the angle φ, so that no change in the previously exactly set register results from this angular adjustment and, following the closure of the embosser, the register controller (which is started after the pre-registration or preferably with the closure of the embosser) ensures that the embossing pattern is immediately printed in register and thus no rejects are produced. 

What is claimed is:
 1. A method for operating a processing machine, comprising: delimiting a first web section of a product web by closing a first clamping point and a second clamping point, such that a first web tensile force prevails in the first web section; closing a third clamping point within the first web section, so that a second web section is formed between the first clamping point and the third clamping point; and adjusting at least one of the closed third clamping point and the closed first clamping point by an angle, so that a second web tensile force in the second web section is changed.
 2. The method according to claim 1, further comprising: calculating the angle from geometric variables of at least one of the first clamping point, the third clamping point, and the second web section.
 3. The method according to claim 2, further comprising: calculating the angle from at least one of (i) a first diameter of a rotating cylinder of the first clamping point, and (ii) a second diameter of a rotating cylinder of the third clamping point.
 4. The method according to claim 2, further comprising: calculating the angle from a product web length of the second web section.
 5. The method according to claim 2, further comprising: calculating the angle from a modulus of elasticity of the product web in the second web section.
 6. The method according to claim 1, further comprising: aligning a processing register of the third clamping point before closing the third clamping point.
 7. The method according to claim 1, wherein a higher web tensile force is introduced into the product web by the third clamping point than by at least one of the first clamping point and the second clamping point.
 8. The method according to claim 1, wherein the second web tensile force in the second web section is regulated to a set point.
 9. The method according to claim 8, further comprising: determining the set point by using data from preceding production runs, wherein the set point is retrievable in a database.
 10. The method according to claim 1, further comprising: regulating a processing register of the third clamping point directly following (i) the closing of the third clamping point or (ii) the changing of the second web tensile force in the second web section.
 11. The method of claim 1, wherein a computing unit is configured to carry out the method.
 12. The method of claim 11, wherein a computer program includes a program code configured to cause the computing unit to carry out the method when the program code is executed on the computing unit.
 13. The method of claim 12, wherein the computer program is stored on a machine-readable storage medium.
 14. The method of claim 1, wherein the adjusting the at least one of the closed third clamping point and the closed first clamping point by an angle, increases the second web tensile force in the second web section.
 15. A web processing machine, comprising: a computing unit configured to carry out a method, wherein the method includes delimiting a first web section of a product web by closing a first clamping point and a second clamping point, such that a first web tensile force prevails in the first web section, closing a third clamping point within the first web section, so that a second web section is formed between the first clamping point and the third clamping point, and adjusting at least one of the closed third clamping point and the closed first clamping point by an angle, so that a second web tensile force in the second web section is changed. 